传送数据时水平电缆的最大长度为：（）。 A.90米 B.100米 C.140米 D.

Today I visited the Smiths — my first time visit 1.________

to a American family. They live in a small 2 _________

town. It was very kind for them to meet me 3.__________

at the railway station and drove me to their home 4.__________

The Smiths did his best to make me feel 5.__________

at home. They offered me coffee and other 6.__________

drinks. We have a good time talking and laughing 7.__________

together. They eager to know everything about 8.__________

China and asked me lots of question. In fact, 9 .__________

they are planning to visit China in next year. 10.__________

下面关于RS-232标准的叙述中，错误的是( )。

A．PC 机串行接口的电气规范与USB标准的电气规范一致

B．RS-232标准采用负逻辑，即逻辑1电平为-5V～15V；逻辑0电平为+5V～+15V

C．RS-232标准的逻辑电平与TTL/CMOS逻辑电平不兼容

D．数据终端设备皿和数据通信设备DCE采用RS-232标准时，它们的引脚具有相同的名称，但同名引脚的信号流向相反

证券登记结算机构是以营利为目的的法人。( )

在CAD中以下有关多边形的说法错误的是（）

A．多边形是由最少3条至多1024条长度相等的边组成的封闭多段线

B．绘制多边形的默认方式是外切多边形

C．内接多边形绘制是指定多边形的中心以及从中心点到每个顶角点的距离，整个多边形位于一个虚构的圆中

D．外切多边形绘制是指定多边形一条边的起点和端点其边的中点在一个虚构的圆中

3个体积硝酸和1体积盐酸的混合溶剂称为王水。